Biodiesel is an alternative fuel based on renewable resources, most commonly vegetable oil. Biodiesel itself contains no petroleum, but is typically blended with petroleum diesel to create a Biodiesel blend.
The term Biodiesel is generally used to describe the output of a thermodynamic process where the glycerin component of vegetable oil is separated and removed from the ethyl or methyl esters of the source oil. The glycerin component of vegetable oil is normally considered a negative because its presence raises the viscosity and flash point of vegetable oil to levels that are incompatible with commonly used diesel engines.
Biodiesel offers several benefits over typical fossil fuels. These benefits include cleaner burning and the fact that it can be produced from available renewable resources.
Biodiesel, however, also has many drawbacks. For example, the process of producing Biodiesel is capital intensive and time consuming. The Biodiesel process also has ecological negatives, primarily in the form of pollutant byproducts.
Further, Biodiesel may not be 100% compatible with petroleum diesel in the areas of flash point, viscosity, cetane rating, and cold weather performance, among others. Accordingly, Biodiesel is typically blended with petroleum diesel to allow it to be used in vehicles that have not been modified for the use of pure Biodiesel.
The typical Biodiesel process begins by taking, for example, ten gallons of used vegetable oil. The oil is first filtered to remove food particulates in the oil. Methanol and lye are then added to the oil. The mixture is heated for a period of time, often several hours, to a temperature generally between 48 and 54 degrees C. The solution is then allowed to cool, generally for 8 hours or longer, during which the heavier glycerin component precipitates out of the solution. The methyl esters—the Biodiesel—are then skimmed off of the top of the solution. Generally, a little over 60 vol. % of the solution will be refined Biodiesel fuel. The glycerin by-product is approximately 8 vol. % by volume of the original oil. Next, the Biodiesel fuel is cleaned with water to remove any remaining lye. If the lye is not completely removed from the fuel it can corrode certain types of vehicle fuel lines and, potentially, clog fuel filters. Finally, the Biodiesel is cleaned and dried in a process that separates water and residual impurities from the pure Biodiesel. Among the pollutant byproducts of this process is water tainted with lye.